1. Field of the Invention
The present invention relates generally to transistors, and more specifically to a transistor collector structure for improved matching and power supply connection.
2. Description of the Prior Art
Throughout the history of transistor design, the power supply has been applied to a transistor collector by a variety of means, depending on the particular circuit application and frequency of operation desired. Common means for supplying power to the transistor collector have included an RF choke, a section of transmission line, and an inductance of a resonance circuit.
In the case where a transmission line or RF choke is used, their parameters must be chosen carefully, usually resulting in compromise. For in-band frequencies, the transmission line or RF choke should not load the collector or throw the transistor into oscillations. For out-of-band frequencies, the transistor must remain stable. In broadband applications, these requirements become even more critical and difficult to achieve. The use of an RF choke can adversely affect achievement of these design goals. For instance, at low frequencies where power gain is high, the inductance represented by the RF choke may contribute to circuit instability.
In addition to transistor stability, matching between the load internal to the transistor and the external load, usually 50 ohms, is an important design consideration. A fixed shunt inductance, typically internal to the transistor, is commonly used in transistor power designs as part of the transistor output matching circuit. It provides the benefit of tuning out the effective output capacitance of the transistor, thereby decreasing the transformation ratio required of matching circuitry and increasing transistor efficiency.
Since the value of the fixed shunt inductance is normally predetermined before the transistor is fabricated, it may be that this value is not optimal for a given transistor application. Therefore, the predetermined shunt inductance provides the designer very little flexibility.